As is known in the art, speed detection systems may be used to determine the speed of moving objects, such as ground based or airborne motor vehicles for example. It is often desirable for the operator of the moving vehicle to know when the speed of the vehicle is being measured. For example, it may be desirable for an operator of a moving automobile to know when the speed of the automobile is being detected by a speed detection system.
As is also known, such speed detection systems may utilize either radar or laser devices in their operation. A speed detection system which utilizes radar may generally be referred to as a so-called radar gun. Radar guns typically include a microwave signal source which emits a signal having a frequency in either the X, K or Ka frequency regions of the electromagnetic spectrum. Furthermore, radar guns may emit signals in either a continuous or a pulsed mode.
A laser speed detection system or so-called laser gun, on the other hand, includes a laser which is a device that converts input power into a very narrow, intense beam of coherent energy at a single optical frequency, generally, but not necessarily, within the visible to infrared frequency region of the electromagnetic spectrum. Like radar guns, laser guns may also operate either continuously or in a pulsed mode. Laser guns generally operate in a pulsed mode due to input power requirements, cooling problems, and other considerations of the laser. The pulse width of the output of a pulsed laser is typically on the order of nanoseconds or picoseconds.
As is also known, there exists two particular classes of detecting systems generally referred to as radar detectors and laser detectors. A radar detector is a device used to detect the presence of a radar gun. A laser detector, on the other hand, is a device used to detect the presence of a laser gun. Typically, devices which detect the presence of radar guns are unable to detect the presence of laser guns. Similarly, devices capable of detecting the presence of laser guns are unable to detect the presence of radar guns.
Radar detectors typically detect signals having frequencies in the X-band, K-band and Ka-band frequency ranges. Such radar detectors often include a fixed frequency oscillator which generates a signal in the X-band frequency range. The so-called third harmonic of some X-band signals, however, fall generally within the Ka-band frequency range. Thus, one problem with conventional radar detectors which detect signals in the Ka-band frequency range is that such radar detectors may provide an alarm in response to the third harmonic signal of the fixed frequency oscillator of a nearby radar detector rather than in response to a signal emitted from a radar gun. This is generally referred to as a "false alarm" or simply "falsing."
For example, the third harmonic signal of a fixed frequency dielectric resonant oscillator (DRO) having a fundamental signal at a frequency of 11.550 GHz is a signal having a frequency of 34.650 GHz. Thus, conventional radar detectors having Ka-band detection capability detect the 34.650 GHz signal and sound false alarms in response thereto.
Laser detectors also have problems with sounding false alarm signals in response to light signals emitted from sources other than laser guns. Laser detectors may also pose an additional problem in that they may be expensive, and may require accurate or pre-determined alignment or positioning of the laser detector within the path of a laser beam in order to function properly. Such systems are thus impractical for use by personnel on moving airborne and ground-based vehicles.
It would, therefore, be desirable to provide a detection device which detects the presence of both laser and radar speed detection systems and which is able to distinguish between signals provided from speed detection systems and signals provided from other detection devices such as other radar detectors.